1. ICMP Message Processing
Homework Assignment #2
ICMP Message Processing

2. Homework Assignment #2: ICMP Message Processing
In this work, you are asked to use timestamp request/reply message to simulate the ping function and calculate the RTT value
Write a program that send a ICMP timestamp request packet to a host, and receive ICMP timestamp reply packet
Furthermore, also calculate the round-trip time (RTT)

3. Flowchart Start Establish socket Establish ICMP packet Header:
#include <sys/types.h>
#include <sys/socket.h>
Define:
int socket(int domain,int type,int protocol)
The third parameter, Protocol, is ICMP
Establish
socket
Header:
#include <netinet/ip_icmp.h>
struct icmp *icmp_hdr=(struct icmp *)buffer;
//#define ICMP_TIMESTAMP
icmp_hdr->icmp_type=13;
icmp_hdr->icmp_code=0;
Establish
ICMP
packet

4. Flowchart (cont.) Receive ICMP reply Calculate RTT
Use sendto() function
Ex.
sendto(sockfd,buffer,packsize,0,(struct sockaddr*)&addr,addr_len)
Send
ICMP
request
Use recvfrom() function
Ex.
recvfrom(sockfd,rbuf,sizeof(rbuf),0,NULL,NULL)
Receive
ICMP
reply
struct icmp *icmp_hdr_R=(struct iphdr*)(rbuf+20);
28~31 byte : original time(T1)
32~35 byte : receive time(T2)
36~40 byte : transmit time(T3)
You need calculating back time by yourself (use time.h)(T4)
RTT= (T4-T3) + (T2-T1)
Calculate
RTT

5. Executable Command Format: myping [addr] Ex. #myping 140.120.15.125
icmp_type= 13,icmp_code=0
Original time=
Receive time=
Transmit time=
Back time=
RTT=
icmp_type=14,icmp_code=0
Receive time=
Transmit time=
Back time=
RTT=6

6. Turn In
Source code
Executing result (snapshot)

7. Turn In (cont.) Deadline Ftp Filename If you want to update
23:59, May 16, 2005
Ftp
IP:
Username/Password: comm93/comm93
Filename
HW2_ID.doc eg.HW2_ doc
If you want to update
HW2_ID_new1.doc, HW2_ID_new2.doc …etc

8. Turn In (cont.) No late work is acceptable No cheat work is acceptable
You get zero if you miss the due day
No cheat work is acceptable
You get zero if you copy other people’s version

9. Reference Linux C/C++ 網路程式設計,金禾 Linux C 函式庫參考手冊,旗標
Linux Socket Programming,碁峰